ATCF – Access Transfer Control Function
The ATCF (Access Transfer Control Function) was introduced in Release 10 of the 3GPP specifications in order to reduce the voice interruption delay when conducting an SRVCC procedure. The ATCF acts as an anchor point for SIP signalling and sits between the P-CSCF and the I-CSCF/S-CSCF in the signalling flow. Moreover, the ATCF controls an ATGW (Access Transfer Gateway), which also acts as an anchor point but in this case for the media stream, as opposed to signalling. In terms of the physical location of the devices, the ATCF could be positioned with the P-CSCF or IBCF.
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